The present invention relates to a liquid crystalline polymer, a liquid crystalline polymer composition and a molded article made of the same.
In these days, demands for high performance plastics are more and more increasing and novel polymers with a variety of functions have been developed. Among those plastics, liquid crystalline polymers which exhibit optical anisotropy have draw the attention because of their excellent mechanical properties. Especially, a liquid crystalline polymer consisting of aromatic polyester which is mainly made up of dominantly parahydroxy benzoic acid or derivatives thereof, is excellent in mechanical and electrical properties as well as in heat resistance and thermal stability, and said liquid crystalline polymer has been applied for a variety of products such as machine components, electric and electronic components, automobile parts and table wears.
The molecules of such liquid crystalline polymer as above are easily oriented with even slight shear strength such as occurred in the injection molding process.
Accordingly, there are some problems in a molded article, such as that difference of the mold shrinkage between in the machine direction (ME)) parallel to a material""s flow in molding and the transverse direction (TD) to the MD, that has high anisotropy in mechanical strength, and that poor strength at the weldline when the article has a weldline.
In order to eliminate the anisotropy at molding, the arts have proposed various methods.
For example, Japanese Patent Publication (KOKOKU) No. 38007/1993 discloses a method for preparation of aromatic polyesters by polycondensing certain compounds, characterized in that compounds having polyfunctional groups such as 1,3,5-trihydroxy benzene, 3,5-dihydroxy benzoic acid, 5-hydroxy isophthalic acid or functional derivatives thereof are added to the reaction system. Japanese Patent Publication No. 38007/1993 teaches that 1,3,5-trihydroxy benzene and the others have less steric hindrance, are highly reactive and are the materials which can provide a polymer with good thermal stability, and that the aromatic polyester obtained by the method exhibits improved molding properties and less anisotropy.
In addition, Japanese Patent Application Laid Open (KOKAI) No, 331275/1993 discloses to improve the weld strength of the polyester resin by adding whisker consisting of needle-like titanium oxide or needle-like aluminum borate thereto.
However, the weld strength improvement effects in the liquid crystalline resins made by the methods as above were not enough and there were another problem that the flowability of the resin was much declined.
Accordingly, the object of the present invention is to dissolve the above-described problems and to provide a liquid crystalline polymer excellent in heat resistance, molding properties, flow properties and mechanical properties, especially to provide a liquid crystalline polymer which can provide a molded article with improved weld strength and less anisotropy in the molding properties.
The present inventors have studied intensively to dissolve the above problems and found that a liquid crystalline polymer made up of certain polyfunctional aromatic monomers can be used to provide a molded article with improved weld strength and less anisotropy.
The present invention provides a liquid crystalline polymer, that is a polymer suitable for melt processing, the main chains of the polymer are regularly aligned in parallel directions to give anisotropic melt phase. The polymer has an optically anisotropic property.
Accordingly, the present invention provide a liquid crystalline polymer which is obtained by copolymerizing at least one polyfunctional aromatic monomer selected from the group consisting of the compounds represented by the general formulae (I), (II) and (III) below: 
wherein Z represents xe2x80x94NHxe2x80x94Axe2x80x94NHxe2x80x94 or xe2x80x94Oxe2x80x94Axe2x80x2xe2x80x94Oxe2x80x94, wherein A and Axe2x80x2 is an optionally substituted hydrocarbon group of 1-20 carbon atoms which may have a heterocyclic moiety, or a heterocyclic group;
R and Rxe2x80x2 may be the same or different and represent a hydrogen atom or a hydrocarbon group of 1-20 carbon atoms;
Y and Yxe2x80x2 may be the same or different and each represents a hydroxy group or a reactive derivative thereof;
Q and Qxe2x80x2 each represents an optionally branched alkyl or alkoxy group of 1-6 carbon atoms, a halogen atom, a nitro group or a nitroso group; and
m and mxe2x80x2 each represents an integer of 0-3 
wherein X represents an optionally substituted hydrocarbon group of 1-20 carbon atoms which may have a heterocyclic moiety, or a heterocyclic group;
R1, R2, R3 and R4 may be the same or different and each represents a hydrogen atom or a hydrocarbon group of 1-20 carbon atoms;
Q and Qxe2x80x2 each represents an optionally branched alkyl or alkoxy group of 1-6 carbon atoms, a halogen atom, a nitro group or a nitroso group; and
m and mxe2x80x2 each represents an integer of 0-3; with at least one polymerizable monomer.
In the present invention, examples of the hydrocarbon group of 1-20 carbon atoms in the definitions of A, Axe2x80x2 and X include alkylene groups, alkenylene groups, and arylene groups such as phenylene and biphenylene groups.
Examples of the hydrocarbon group of 1-20 carbon atoms in the definition of R and Rxe2x80x2 include alkyl groups of 1-6 carbon atoms, especially methyl and ethyl groups, benzyl group, phenyl group and phenacyl group.
The reactive derivative of hydroxy group in the definition of Y and Yxe2x80x2 may be any which can form an ester.
In the following illustration of the present invention, the at least one compound selected from polyfunctional aromatic monomers represented by the general formulae (I), (II) and (III) will be represented as {circle around (1)}.
The at least one polymerizable monomer used in the liquid crystalline polymer of the present invention may be any of the monomers used in conventional liquid crystalline polymers. Examples of the preferable monomers are those described in the {circle around (2)}-{circle around (5)} below.
{circle around (2)}: at least one compound selected from aromatic dicarboxylic acids;
{circle around (3)}: at least one compound selected from aromatic diols;
{circle around (4)}: at least one compound selected from aromatic hydroxycarboxylic acids; and
{circle around (5)}: at least one compound selected from the group consisting of aromatic hydroxyamines, aromatic diamines, aromatic aminocarboxylic acids.
In a preferred embodiment of the present invention, the liquid crystalline polymer of the present invention may be consisting of the combination of following A)-G):
A) a polyester consisting of {circle around (1)}, {circle around (2)} and {circle around (3)};
B) a polyester consisting of {circle around (1)} and {circle around (4)};
C) a polyester consisting of {circle around (1)}, {circle around (2)}, {circle around (3)} and {circle around (4)};
D) a polyester consisting of {circle around (1)}, {circle around (3)} and {circle around (4)};
E) a polyesteramide consisting of {circle around (1)}, {circle around (3)}, {circle around (4)} and {circle around (5)};
F) a polyesteramide consisting of {circle around (1)}, {circle around (2)}, {circle around (4)} and {circle around (5)}; and
G) a polyesteramide consisting of {circle around (1)}, {circle around (2)}, {circle around (3)}, {circle around (4)} and {circle around (5)}.
Further, the liquid crystalline polymer of the present invention may be the one obtained by copolymerizing the above described components with one or more compounds selected from the group consisting of an alicyclic dicarboxylic acid, an alicyclic diol, an aliphatic diol, an aromatic thiol carboxylic acid, an aromatic dithiol, and an aromatic thiol phenol.
Examples of the compounds suitable as monomers used for preparation of the liquid crystalline polymer of the present invention are described below.
The polyfunctional aromatic monomer of {circle around (1)} is the compound represented by the formulae (I), (II) or (III). Particularly, a compound obtained by crosslinking the 3rd position of a 2-hydroxynaphthalene-3,6-dicarboxylic acid derivative with ester and/or amide bondings, such as 1,4-bis(2xe2x80x2-hydroxy-6xe2x80x2-hydroxycarbonylnaphtho-3xe2x80x2-ylcarbonyl amino)phenylene, a compound obtained by crosslinking the 2nd position of a 2-hydroxynaphthalene-3,6-dicarboxylic acid derivative with ether bonding, such as 2,2xe2x80x2-hexylenedioxy-bis(3,6-dihydroxycarbonyl naphthalene), and a compound obtained by crosslinking the 6th position of a 2-hydroxynaphthalene-3,6-dicarboxylic acid derivative with ester and/or amide bondings such as 4,4xe2x80x2-bis(2xe2x80x3-hydroxy-3xe2x80x3-hydroxycarbonylnaphtho-6xe2x80x3-ylcarbonyl)biphenol.
As the at least one polymerizable monomer, the above described {circle around (2)}-{circle around (5)} compounds and oligomers obtained from one or more those monomers are preferably used.
Examples of the aromatic dicarboxylic acids of {circle around (2)} include aromatic dicarboxylic acids and alkyl, alkoxy or halogen substituted derivatives thereof such as terephthalic acid, chloro terephthalic acid, dichioro terephthalic acid, bromo terephthalic acid, methyl terephthalic acid, dimethyl terephthalic acid, ethyl terephthalic acid, methoxy terephthalic acid, ethoxy terephthaiic acid, isophthalic acid, naphthalene-2,6-dicarboxylic acid, naphthalene-1,6-dicarboxylic acid, naphthalene-2,7-dicarboxylic acid, biphenyl-4,4xe2x80x2-dicarboxylic acid, terphenyl-4,4xe2x80x3-dicarboxylic acid, diphenylether-4,4xe2x80x2-dicarboxylic acid, diphenoxybutane-4,4xe2x80x2-dicarboxylic acid, diphenylethane-4,4xe2x80x2-dicarboxylic acid, diphenylether-3,3xe2x80x2-dicarboxylic acid and diphenylethane-3,3xe2x80x2-dicarboxylic acid. Among the above, terephthalic acid, isophthalic acid, naphthalene-2,6-dicarboxylic acid and biphenyl-4,4xe2x80x2-dicarboxylic acid are preferable.
Examples of the aromatic diols of {circle around (3)} include aromatic diols and alkyl, alkoxy or halogen substituted derivatives thereof, such as hydroquinone, chloro hydroquinone, methylhydroquinone, 1-butylhydroquinone, phenylhydroquinone, methoxyhydroquinone, phenoxy hydroquinone, 2,6-dihydroxynaphthalene, 2,7-dihydroxy naphthalene, 1,6-dihydroxynaphthalene, 4,4xe2x80x2-biphenol, 4,4xe2x80x3-dihydroxyterphenyl, 4,4xe2x80x2-dihydroxybiphenyl ether, 3,3xe2x80x2-dihydroxybiphenyl ether, bis(4-hydroxyphenoxy)ethane, 3,3xe2x80x2-biphenol, 2,2-bis(4-hydroxyphenyl)methane, resorcin, 4-chlororesorcin and 4-methylresorcin. Among the above, hydroquinone, methylhydroquinone, phenylhydroquinone, 2,6-dihydroxynaphthalene, 2,7-dihydroxynaphthalene and 4,4xe2x80x2-dihydroxybiphenyl are preferable.
Examples of the aromatic hydroxycarboxylic acid of {circle around (4)} include aromatic hydroxycarboxylic acids and alkyl, alkoxy or halogen substituted derivatives thereof, such as 4-hydroxybenzoic acid, 3-methyl-4-hydroxybenzoic acid, 3,5-dimethyl-4-hydroxybenzoic acid, 2,6-dimethyl-4-hydroxy benzoic acid, 3-chloro-4-hydroxybenzoic acid, 2-chloro-4-hydroxybenzoic acid, 2,3-dichloro-4-hydroxybenzoic-acid, 3-bromo-4-hydroxybenzoic acid, 6-hydroxy-2-naphthoic acid, 6-hydroxy-5-methyl-2-naphthoic acid, 6-hydroxy-5-methoxy-2-naphthoic acid, 6-hydroxy-5-chloro-2-naphthoic acid, 6-hydroxy-7-chloro-2-naphthoic acid, 6-hydroxy-5,7-dichloro-2-naphthoic acid, 3-hydroxy-2-naphthoic acid and 2-hydroxy-3-naphthoic acid. Among the above, 4-hydroxy benzoic acid and 6-hydroxy-2-naphthoic acid are preferable.
Examples of the aromatic hydroxyamines, aromatic diamines, aromatic aminocarboxylic acids of {circle around (5)} include 4-aminophenol, N-methyl-4-aminophenol, 3-aminophenol, 3-methyl-4-aminophenol, 4-amino-1-naphthol, 4-amino-4xe2x80x2-hydroxybiphenyl, 4-amino-4xe2x80x2-hydroxybiphenyl ether, 4-amino-4xe2x80x2-hydroxybiphenyl methane, 4-amino-4xe2x80x2-hydroxybiphenyl sulfide, 1,4-phenylenediamine, N-methyl-1,4-phenylenediamine, N,Nxe2x80x2-dimethyl-1,4-phenylenediamine, 4,4xe2x80x2-diaminosulfide(thiodianiline), 4,4xe2x80x2-diaminobiphenyl sulfone, 2,5-diamino toluene, 4,4xe2x80x2-ethyienedianiline, 4,4xe2x80x2-diaminobiphenoxy ethane, 4,4xe2x80x2-diaminobiphenyl methane(methylene dianiline), 4,4xe2x80x2-diaminobiphenyl ether(oxydianiline), 4-aminobenzoic acid, 3-aminobenzoic acid, 6-amino-2-naphthoic acid, 7-amino-2-naphthoic acid. Among the above, 4-aminophenol, 1,4-phenylenediamine and 4-aminobenzoic acid are preferable.
The above polymers A)-G) comprising the above described components may include those give anisotropic melt phase and those do not, depending on components of the polymer and the ratio thereof, and the sequence distribution. The liquid crystalline polymer of the present invention covers only those give anisotropic melt phase.
The liquid crystalline polymer of the present invention may be prepared by copolymerizing the above component {circle around (1)} with at least one polymerizable monomer. The proportion of the at least one polyfunctional aromatic monomer selected from the group consisting of the compounds represented by the formulae (I), (II) and (III) (i.e. component {circle around (1)}) to the whole monomers consisting the polymer may be 0.01-5 mole %, preferably 0.01-2 mole %, more preferably 0.01-1 mole %.
In order to prepare the liquid crystalline polymer of the present invention, the polyfunctional aromatic monomer component {circle around (1)} may be added to the reaction mixture at the initial stage of the polymerization process; the polymerizable monomers such as {circle around (2)}-{circle around (5)} may be partially pre-polymerized before addition of the component {circle around (1)} and the whole may be polymerized together; or the component {circle around (1)} may be added successively to the mixture of polymerizable monomers while they are under the polymerizing stage before the reaction complete.
The polymerization may be conducted at a temperature of 200-400xc2x0 C., preferably 250-350xc2x0 C.
Examples of the combination of the components consisting of the preferable polymers of the present invention are follows. 
In the above formulae, Z represents xe2x80x94Oxe2x80x94Axe2x80x2xe2x80x94Oxe2x80x94 and/or xe2x80x94NHxe2x80x94Axe2x80x94NHxe2x80x94, wherein A, Axe2x80x2 and X each represents, for example, an alkylene group, a phenylene group and a biphenylene group.
Polyesters and polyesteramides of the present invention, i.e. the liquid crystalline polymers that give anisotropic melt phase can be prepared by a variety of ester and amide forming methods which enable to react organic monomers having functional groups which contribute to form the required repeating unit each other by condensation reaction. Examples of the functional groups of the organic monomers include carboxyl, hydroxy, ester, acyloxy halocarbonyl and amino groups. The above organic monomer compounds may be reacted by means of molten acidolysis method without the presence of heatexchange fluid. In this method, firstly monomers are heated together to give molten solution of the reactant. Upon the reaction proceeds, oligomer particles appear in the reaction media to give suspension. In order to facilitate the removal of volatile materials (ex. acetic acid or water) occurs at the final stage of the condensation reaction, the reaction may be carried out under vacuum.
In order to prepare the whole aromatic polymer useful for the present invention, the solid phase polymerization method may also be applied. In this method, the solid products may be polymerized as fine particles in a fluidized or still stood fashion, or may be polymerized by suspending in a heatexchange medium.
The organic monomer reactants, which provide the whole aromatic polymer, may be subjected to either the molten acidolysis or solid phase polymerization as modified compounds wherein the hydroxy groups of the monomers are esterified (i.e. as lower acyl esters) at an ambient temperature. The lower acyl group may have preferably 2-4 carbon atoms. In addition, acetates of said organic monomers are also preferably subjected to the reaction.
Examples of catalysts which may optionally be used in either the molten acidolysis process or the solid phase polymerization process include monoalkyl tin oxide (ex. monobutyl tin oxide), dialkyl tin oxide (ex. dibutyl tin oxide), diaryl tin oxide, titanium dioxide, antimony trioxide, alkoxy titanium silicate, titanium alkoxide, an alkaline or alkaline earth metal salt of an carboxylic acid (ex. zinc acetate), and gaseous acid catalysts such as a Lewis acid (ex. BF3) and halogenated hydrogen (ex. HCl). The amount of the catalyst to be used may be 0.01-1 wt %, preferably 0.02-0.2 wt % of total amount of the monomers.
The liquid crystalline polymers of the present invention show a tendency that they are substantially insoluble to conventional solvents, and therefore, they are not suitable for the solution casting. However, as already mentioned above, those polymers are easily processed by means of a conventional melt molding. Some of the most preferable whole aromatic polymers exhibit some solubility in pentafluoro phenol.
The liquid crystalline polymers obtained according to the present invention may be admixed, if desired, with various reinforcing agents, fillers and stabilizers, and colorant to the extent that they do not impair the object of the present invention. The amount of the reinforcing materials and fillers to be added may be about 1-60 wt %. Examples of reinforcing materials, fillers and stabilizes, and colorant include glass fiber, carbon fiber, aramid fiber, silica, talc, mica, wollastonite, clay, aluminum borate whisker, potassium titanate whisker, glass flake, powdery quarts, sands, fumed silica, silicon carbide, aluminum oxide, tin oxide, iron oxide, zinc oxide, graphite, titanium dioxide and carbon black. In addition, the polymer may contain additives such as nucleating agent, anti oxidant, stabilizer, lubricant, releasing agent and flame retardant, to the extent that those additives do not deteriorate the object of the present invention.
The liquid crystalline polymer of the present invention may be subjected to a three-dimensional molding process, for example, injection molding, extrusion molding and blow molding, fiber spinning or film casting carried out under the condition where the cylinder temperature is above the liquid crystal state initiation temperature, preferably above the temperature of (liquid crystal state initiation temperature +10xc2x0 C.) but below the point where the polymer is decomposed. Accordingly, the polymer may provide a molded article with good dimensional accuracy.